JP5127378B2 - Aluminum nitride sintered body and substrate mounting apparatus using the same - Google Patents

Description

The present invention relates to a substrate mounting apparatus used in a semiconductor manufacturing apparatus and a flat panel display manufacturing apparatus.

Ceramic substrates have been used in many processes as substrate mounting devices such as semiconductor process heaters. This is because the thermal, electrical and mechanical properties of ceramics are suitable for these processes. In particular, ceramics are advantageous because they are excellent in wear resistance and have few particles due to contact with the substrate. In recent years, the demand for low particle properties has become very strict, and it is difficult to satisfy the demand only by using ceramics. For this reason, the contact area with the substrate has been reduced (for example, Patent Document 1). ).
JP-A-5-267436

However, if the contact area is small, the thermal response when heating the substrate is lowered, which is a problem. To solve this problem, gas is convected and heated in a space formed between the base and the substrate by a protrusion provided to reduce the contact area, but the substrate processing efficiency is increased. For this purpose, it has been demanded to further improve the thermal responsiveness.

In addition, the substrate processing process includes not only heating but also cooling. For example, in the case of performing plasma etching, the input energy is changed to heat, so that the substrate generates heat. In this case, in order to perform the etching process under a certain condition, the substrate is cooled by flowing a coolant through the substrate mounting apparatus. Even in such a case, it is possible to control the temperature of the substrate with high accuracy by increasing the thermal responsiveness during cooling.

Thus, in the substrate mounting apparatus, thermal responsiveness is required at the same time as low particle property, but if the contact area is reduced for particle reduction, the thermal responsiveness will be lowered. It has been difficult to achieve both compatibility and thermal responsiveness.

The present invention solves these problems, and provides a substrate mounting apparatus that generates less particles and has excellent thermal response.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have made the following invention.

That is, in the present invention, the aluminum nitride content is 99.4% by volume or more, the surface roughness Ra is 0.01 to 0.1 μm, and the total emissivity at 200 ° C. is 60% or more. A base made of an aluminum nitride sintered body, and a protrusion formed on the surface of the base and on which the substrate is placed, and the total emissivity of the base at 200 ° C. is the tip of the protrusion The substrate mounting apparatus is characterized by being larger than the total emissivity at 200 ° C. If aluminum nitride having a high total emissivity is used, a substrate mounting device having excellent thermal response can be obtained. In addition, since the total emissivity in the operating temperature range of 200 ° C. or higher is large, sufficient thermal responsiveness can be exhibited even in a high temperature range.

It is preferable that the substrate mounting device further includes a heating resistor embedded in the base body or exposed on the side opposite to the surface .

The substrate mounting apparatus of the present invention is suitably used for a processing step in which the substrate is 200 ° C. or higher. Since the thermal conductivity of ceramics decreases as the temperature rises, the effect of radiation from the non-contact portion becomes greater with respect to the heat conduction at the contact portion with the substrate. Moreover, it has been found that the thermal response is high when the radiation of the non-contact part is larger than the radiation of the contact part as in the substrate mounting apparatus of the present invention. This is because the effect of radiation is greater at higher temperatures than heat conduction by direct contact. This effect is particularly effective for heating and cooling under reduced pressure with a small contact area with the substrate and a small heat medium.

About the emissivity of a base | substrate, the thermal responsiveness of a board | substrate can be improved by making it larger than the total emissivity of a front-end | tip part. Therefore, sufficient soaking can be achieved by radiation from the substrate without using a soaking gas, and soaking can be achieved more efficiently even when a soaking gas is used. .

Furthermore, by increasing the total emissivity of the substrate, the temperature difference between the tip of the protrusion on which the substrate is placed and the substrate can be quickly reduced. As a result, the stress concentration on the tip of the protrusion due to the difference in thermal expansion can be suppressed. As a result, the combined stress of mechanical stress and thermal stress due to contact with the substrate can be reduced, so the generation of particles can be reduced It becomes.

According to the present invention, an aluminum nitride sintered body having a high total emissivity at a high temperature and suitable for a substrate mounting apparatus is provided, and a low particle property substrate mounting having sufficient thermal response even in a high temperature region. An apparatus can be provided.

In the aluminum nitride sintered body of the present invention, the aluminum nitride content is desirably 90% by volume or more. If the aluminum nitride content is less than 90% by volume, the total emissivity is abruptly lowered, which is not preferable. In order to increase the thermal conductivity, aluminum nitride often adds a sintering aid made of an oxide of a 2a group element or a 3a group element. Generally, the amount of the sintering aid added increases the thermal conductivity, but it is known that the addition of a certain amount or more causes a decrease in the thermal conductivity. However, according to the study by the present inventors, when the content of the sintering aid composed of the oxide of group 2a element or group 3a element exceeds a certain amount, not only the thermal conductivity decreases but also the total emissivity. It was found that a decrease in the temperature also occurred. Therefore, it is desirable that the content of the sintering aid composed of the oxide of the group 2a element or the group 3a element is 10% by volume or less. Examples of the additive of the group 2a element include Mg, Ca, Sr, and Ba, and examples of the additive of the group 3a element include Y, La, Sm, and Ce.

On the contrary, it was found that if aluminum nitride is 90% by volume or more, the addition of a substance that has a lower total emissivity than aluminum nitride and does not react with aluminum nitride has no effect. Examples of such a substance include titanium nitride, titanium carbide, silicon carbide, carbon, tungsten, molybdenum, and the like. By adding such a substance, it is possible to control the thermal conductivity, volume resistivity, strength, and the like of aluminum nitride while maintaining a high total emissivity. The content of these additives is preferably 10% by volume or less like the sintering aid.

The aluminum nitride content at the tip of the protrusion that contacts the substrate is desirably 90% by volume or more, as with the substrate, but may be less than the aluminum nitride content of the substrate.

Hereinafter, with reference to the drawings, a ceramic heater will be taken up as an example of the substrate mounting apparatus of the present invention and described in more detail. FIG. 1 is a cross-sectional view showing a schematic configuration of a ceramic heater according to an embodiment of the present invention. The ceramic heater 1 has a plurality of pin-shaped protrusions 2 on which the substrate is placed on the placement surface side of the base 2. The heights of the protrusions 2 are substantially the same, and the front end portions of the protrusions are flattened, and the substrate W is placed on the front end portions.

The total emissivity of aluminum nitride is controlled by adjusting the surface roughness of the aluminum nitride sintered body in addition to the content of aluminum nitride, the kind of additive, and the amount added as described above. be able to. The surface roughness Ra (JIS B0601) is preferably adjusted in the range of 0.01 to 3. This is because if it is smaller than 0.01, the total emissivity at 200 ° C. does not become 60% or more. On the other hand, if it is larger than 3, the number of particles is remarkably increased, which is not preferable. The total emissivity here refers to the emissivity at a wave number of 400 to 6000 cm ⁻¹ .

As a method of controlling the total emissivity of the tip of the protrusion and the base, the base part and the tip may be adjusted at the time of molding the base, or the base part and the tip may be prepared with the same composition. The surface roughness may be adjusted.

The ceramic heater of the present invention can be variously modified without being limited to the above embodiment. For example, the size, height, number, and arrangement of the protrusions are not limited and may be arbitrarily selected. Furthermore, the outer shape of the mounting portion may be selected according to the shape of the mounting substrate, such as a circle or a rectangle.

The shape of the protrusion is not particularly limited, such as the above-described pin shape, ring shape, lattice shape, mesh shape, or a combination thereof. However, as described above, since the contact area between the substrate and the tip portion should be small, the pin shape is most desirable. As the pin shape, various shapes such as a prism and a cylinder can be adopted, and the contact area with the substrate is desirably 10% or less of the area of the substrate.

The height of the protrusion is not particularly limited, but is desirably 5 to 50 μm. In addition to radiation from the substrate, when trying to improve the thermal responsiveness by flowing He gas between the ceramic heater and the substrate as a heating medium, the substrate will be detached from the ceramic heater unless the substrate is fixed. It is necessary to provide an electrostatic chuck function to the heater and to electrostatically fix the substrate. At this time, if the height of the protrusion is smaller than 5 μm, the convection of He gas may be insufficient, which may be disadvantageous for the thermal response. In this case, the heat uniformity is also significantly reduced. In addition, if the height of the protrusion is larger than 50 μm, the electrostatic attractive force is abruptly decreased, so that the substrate is easily detached from the ceramic heater.

The method for forming the protrusions on the substrate is not particularly limited, and a method of forming a mask on a portion where the protrusions are to be formed and blasting the mask, or a method of performing etching treatment or machining can be employed.

Further, the portion other than the mounting surface of the base on which the protrusions are formed may be the same ceramic as the base, or may be other ceramics, metal, a composite material of metal and ceramics, or the like. Therefore, as a method for producing ceramics, well-known methods such as thermal spraying, CVD, and AD methods can be adopted in addition to sintering methods such as normal pressure and hot pressing.

In order to obtain a predetermined total emissivity, it is desirable that the relative density is 98% or more and the porosity is 0.5% or less. Outside this range, particles are more likely to be generated than in the range. Accordingly, the relative density is preferably larger and the porosity is preferably smaller.

As the heating resistor, a heat-resistant metal such as tungsten or molybdenum can be used. Even if it is embedded in the base made of an aluminum nitride sintered body, it may be exposed on the surface (surface opposite to the mounting surface). For example, a heating resistor such as a plate, foil, wire, or net may be embedded and sintered at the time of molding, or a paste of heat-resistant metal powder may be applied to an aluminum nitride sintered body and baked.

Furthermore, as an embodiment of the substrate mounting apparatus of the present invention, a cooling medium is provided inside the base in addition to the ceramic heater provided with a heating resistor inside or on the surface made of the aluminum nitride sintered body as described above. It can also be applied to a mounting device that cools the substrate and, for example, an aluminum nitride electrostatic chuck used for etching. Since a substance having a high emissivity has a good absorption rate, an effect of absorbing heat from a wafer heated during etching and maintaining a constant temperature condition of the etching process can be expected.

Furthermore, even in the cooling device as described above, by increasing the total emissivity of the substrate, the temperature difference between the tip of the protrusion on which the substrate is placed and the substrate can be quickly reduced. Generation of particles can be reduced because thermal stress is suppressed and composite stress combining mechanical stress and thermal stress due to contact with the substrate can be reduced.

Yttrium oxide was added to aluminum nitride to prepare a raw material powder having a predetermined aluminum nitride content (Table 1). Next, CIP molding was performed using this raw material powder, and the obtained molded body was fired in a reducing atmosphere to obtain a sintered body of 100 × 100 × 10 mm. These sintered bodies were ground and polished so as to have a predetermined surface roughness. The total emissivity of the obtained sintered body was measured using a Fourier transform infrared spectrophotometer and an integrating sphere. The results are shown in Table 1. Note that the measurement region has a wave number of 400 to 6000 cm ⁻¹ .

In Test Examples 1 to 5, an aluminum nitride sintered body having a total emissivity at 200 ° C. of 60% or more was obtained. On the other hand, in Test Examples 6 and 7, the total emissivity at 200 ° C. was smaller than 60%.

Next, the present invention will be described in more detail with reference to examples of ceramic heaters. By using a raw material powder obtained by adding yttrium oxide to an aluminum nitride powder so that the aluminum nitride content of No. 1 and No. 7 in Table 1 is obtained, a heating resistor made of molybdenum is embedded and fired to obtain φ210 × 10 mm A sintered body was obtained. Each sintered body had a relative density of 99% and a porosity of 0.5%.

Next, this sintered body was subjected to cylindrical and surface grinding to process the insulating layer thickness to 1 mm and the outer shape to φ200 × 8 mm. Further, lapping was performed so that the flatness of the surface on which the placement surface is formed is 3 μm or less. Next, a pin pattern mask having a diameter D of 0.5 mm, a spacing P of 2 mm, and a staggered 60 ° as shown in FIG. 2 was applied to the insulating layer, and pin-shaped protrusions having a height of 30 μm were formed by blasting. The tip of the protrusion and the substrate were polished by using a chemical fiber cloth polishing disk and polishing using a grinding liquid mixed with abrasive grains, and the surface roughness Ra was adjusted to a predetermined emissivity.

After that, lapping using a polishing surface plate was performed on the tip of the protrusion, and the flatness of the flat surface made up of the protrusion tip was adjusted to 1 μm or less. A bottomed hole for connecting a power supply terminal to the heating resistor was processed on the surface opposite to the mounting surface to expose the heating resistor, and the heating resistor and the terminal were connected by brazing.

The heater is placed in a vacuum, a voltage is applied to the heating resistor through the power supply terminal to heat the ceramic heater to 400 ° C., and a wafer at room temperature (23 ° C.) is placed thereon. The time required to reach ° C was compared for each heater. Moreover, the particle | grains of the 0.2-1.0 micrometer size adhering to the wafer were implemented by the laser scattering type foreign material inspection apparatus. The results are shown in Table 2.

In Test Examples 8 to 10 where the emissivity of the substrate at 200 ° C. was 60% or more, the time until the wafer reached 400 ° C. was early, and the number of particles was small. On the other hand, in Test Examples 11 and 12 where the emissivity of the substrate was less than 60%, the time until the wafer reached 400 ° C. was longer than Test Examples 8-10. Further, more particles were generated than in Test Examples 8 to 10.

As described above, according to the present invention, it has been shown that a substrate mounting apparatus that has sufficient thermal responsiveness even in a high temperature range and that suppresses generation of particles can be provided.

It is a schematic cross section of a ceramic heater. It is a top view which shows the example of arrangement | positioning of a pin-shaped protrusion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Ceramics heater 2; Protrusion 3; Base | substrate 4; Heating resistor 5; Bottomed hole 6;

Claims (2)

From an aluminum nitride sintered body having an aluminum nitride content of 99.4% by volume or more, a surface roughness Ra of 0.01 to 0.1 μm, and a total emissivity at 200 ° C. of 60% or more. And a projection formed on the surface of the substrate and on which the substrate is placed . The total emissivity of the substrate at 200 ° C. is the total radiation of the projection at the tip of the projection at 200 ° C. A substrate mounting apparatus characterized by being larger than the rate . The substrate mounting apparatus according to claim 1 , further comprising a heating resistor embedded in the base body or exposed on a side opposite to the surface.

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